There are an estimated 8.7 million species of plants, animals, and other organisms on Earth, according to a new tally of life on our planet.  Previous estimates of the number of species had ranged from 3 million to 100 million. The study was completed by scientists at Dalhousie University in Canada using a mathematical model based on the number of known species.

The scientists calculated that there are about 7.77 million species of animals; 298,000 species of plants; 611,000 species of fungi; 36,400 species of protozoa; and 27,500 species of chromists (organisms that are mostly ocean dwelling and make their own food using sunlight). However, only about 1.3 million species have actually been named and classified. The Dalhousie scientists estimated that 86 percent of all land-based species and 91 percent of all marine species remain unknown and so have not been described or catalogued.

Marine biologist Boris Worm, one of the study’s co-authors, compared Earth to a machine with 8.7 million parts in an article on the research in The Washington Post. “If you think of the planet as a life-support system for our species, you want to look at how complex that life-support system is,” Worm is quoted as saying. “We’re tinkering with that machine because we’re throwing out parts all the time.” The International Union for the Conservation of Nature and Natural Resources, a global federation of government and private conservation organizations, has estimated that at least one-third of Earth’s species are threatened with extinction.

Additional World Book articles:

• Why Species are Important (special report)